In scanning probe microscopes, or SPMs, a cantilever having a probe located at as small a distance from the sample surface as the atomic level is oscillated at its mechanical resonance frequency, and the interaction between the probe and the sample surface is detected. An atomic-level image of the sample surface can be obtained by detecting the aforementioned interaction while changing the relative position of the sample and the probe. Atom manipulators also use a probe positioned close to the sample surface. After the probe is positioned at a certain distance from the sample, a predetermined manipulation is performed on an atom on the sample surface.
Known examples of the interaction to be detected between the sample and the probe in the SPM or similar apparatus include the tunneling current, interaction forces between atoms (which is hereinafter referred to as “interatomic forces”) (chemical bond force, van der Waals force, covalent bond force, ionic bond force, metallic bond force, electrostatic force, magnetic force, exchange force, etc.), capacitors and the near-field light. In general, obtaining one image by detecting one of these interactions takes anywhere from a few minutes to ten minutes or longer.
If heat is exchanged between the measuring apparatus and the surroundings in the middle of recording the sample image, the sample expands or shrinks (i.e. thermal drift). At room temperature, even in a space where the temperature is controlled, it is impossible to completely maintain the overall temperature of the measuring apparatus at the same level, so that the thermal drift is inevitable. Another problem exists in that the relative position of the sample and the probe can change due to a creep of the piezoelectric element used for changing the relative position between them. Since the measurement is performed at the atomic level, the change in the measurement position caused by a thermal drift or creep significantly affects the measurement result. For example, an image that is supposed to be as shown in FIG. 12(d) can be resultantly distorted as shown in FIG. 12(c). Such effects of the thermal drift or similar variance can not only take place in a direction parallel to the sample surface (XY plane) but also in the direction perpendicular to that surface (Z-direction).
If the sample to be measured is a solid whose surface has a highly symmetrical, well-known structure, any distortion of the image can be immediately recognized by sight, so that there is no serious problem. However, in the case of measuring a biological sample or similar matter whose surface geometry is rather asymmetrical, if an effect of a thermal drift, migration or other variance is present on the image, it is impossible to recognize and/or separate that effect. Therefore, it is practically infeasible to correctly measure the surface geometry. For the atom manipulator, a distortion of the image causes a shift of the target atom within the image, which impedes the correct manipulation of the atom.
A technique for compensating for the effect of a thermal drift or other variances to accurately position the probe and the sample is disclosed in Non-Patent Document 1. This technique, called the atom-tracking technique, corrects the thermal drift in a direction parallel to the sample by a feedback process. Recent studies have demonstrated that the interaction or potential between the probe and the atoms on the sample surface can be measured by performing ultra-precise three-dimensional positioning of the probe in relation to the sample while monitoring the change in the frequency of the probe by the atom-tracking technique (Non-Patent Documents 2 and 3).
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2006-289542
[Non-Patent Document 1] D. W. Pohl and R. Moeller, “Tracking tunneling microscopy”, Review of Scientific Instruments, vol. 59(1988), p. 840
[Non-Patent Document 2] M. Abe et al., “Room-temperature reproducible spatial force spectroscopy using atom-tracking technique”, Applied Physics Letters, vol. 87(2005), p. 173503
[Non-Patent Document 3] M. Abe, Y. Sugimoto, O. Custance and S. Morita, “Atom tracking for reproducible force spectroscopy at room temperature with non-contact atomic force microscopy”, Nanotechnology, vol. 16(2005), p. 3029
Thus, an objective of the present invention is to provide a technique for eliminating the effect of the thermal drift or other variances and to improve the observing or manipulating accuracy of a scanning probe microscope or atom manipulator by using the technique to correct the aforementioned change in the relative position of the probe and the sample due to heat or other factors during the observation or manipulation.